1. Field of the Invention
This invention relates to a Rapid Thermal Processor for heating a substrate. More particularly, this invention relates to a Rapid Thermal Processor for performing temperature compensation with an inverted-cone susceptor.
2. Description of Prior Art
Referring to FIG. 1, a cross-sectional view shows the inner structure of a Rapid Thermal Processor (RTF) 1. The RTP 1 mainly comprises a reaction chamber 10, a holder 11 located in the reaction chamber 10 for supporting the wafer 2, a heater 12, and a gas distributor 13 for distributing the reaction gas 14 flowing into the reaction chamber 10. The wafer 2 or a substrate is supported by the holder 11 located in the reaction gas 14, and the heater 12 is used to generate heat applied to the front surface 21 of he wafer 2. In general, halogen lamps are used as the heater 12, and O.sub.2, N.sub.2, N.sub.2 O, or NH.sub.3 gas is commonly used as the reaction gas in the heat treatment of the wafer 2. Cooling tubes 15, comprising an air-cooled tube 151 and a water-cooled tube 152 wound around the outer sidewall of the reaction chamber 10, are used to reduce the temperature of the reaction chamber 10. A thermocouple 16 controlled by a temperature controller 160 is installed in the reaction chamber 10 and used to sense the temperature in said reaction chamber 10.
When the halogen lamps 12 are energized, heat is applied to the upper surface 21 of the wafer 2 and soon transmitted to the back surface 22. However, the heat absorption rate on the front surface of the wafer 2 is not uniform. There is nearly a 40 percent temperature difference between the central area and the periphery of the wafer 2, as measured by experiment. In addition, when the wafer 2 is fully heated, the average temperature of the holder 11 is much less than that of the wafer 2. Therefore, a large temperature difference exists between the wafer 2 and the holder 11, and heat stress and thermal gradients are easily formed in the wafer 2.